1. Field of the Invention
The present invention pertains generally to telecommunications, and particularly to a High Speed Downlink Packet Access (HSDPA) system such as that operated (for example) in a Universal Mobile Telecommunications System (UMTS) terrestrial radio access network (UTRAN).
2. Related Art and Other Considerations
In a typical cellular radio system, mobile terminals (also known as mobile stations and mobile user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology.
As wireless Internet services have become popular, various services require higher data rates and higher capacity. Although UMTS has been designed to support multi-media wireless services, the maximum data rate is not enough to satisfy the required quality of services.
In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. One result of the forum's work is the High Speed Downlink Packet Access (HSDPA). See, e.g., 3GPP TS 25.435 V6.2.0 (2005-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iub Interface User Plane Protocols for Common Transport Channel Data Streams (Release 6), which discusses High Speed Downlink Packet Access (HSDPA) and which is incorporated herein by reference in its entirety. Also incorporated by reference herein as being produced by the forum and having some bearing on High Speed Downlink Packet Access (HSDPA) or concepts described herein include: 3GPP TS 25.425 V6.2.0 (2005-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iur interface user plane protocols for Common Transport Channel data streams (Release 6); and 3GPP TS 25.433 V6.6.0 (2005-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iub interface Node B Application Part (NBAP) signaling (Release 6).
High Speed Downlink Packet Access (HSDPA) is discussed in one or more of the following (all of which are incorporated by reference herein in their entirety):
U.S. patent application Ser. No. 11/024,942, filed Dec. 30, 2004, entitled “FLOW CONTROL AT CELL CHANGE FOR HIGH-SPEED DOWNLINK PACKET ACCESS”;
U.S. patent application Ser. No. 10/371,199, filed Feb. 24, 2003, entitled “RADIO RESOURCE MANAGEMENT FOR A HIGH SPEED SHARED CHANNEL”.
PCT Patent Application PCT/SE2005/001247, filed Aug. 26, 2005;
PCT Patent Application PCT/SE2005/001248, filed Aug. 26, 2005.
The HSDPA system provides, e.g., a maximum data rate of about 10 Mbps. FIG. 6 illustrates a high-speed shared channel concept where multiple users 1, 2, and 3 provide data to a high speed channel (HSC) controller that functions as a high speed scheduler by multiplexing user information for transmission over the entire HS-DSCH bandwidth in time-multiplexed intervals (called transmission time intervals (TTI)). For example, during the first time interval shown in FIG. 6, user 3 transmits over the HS-DSCH and may use all of the bandwidth allotted to the HS-DSCH. During the next time interval, user 1 transmits over the HS-DSCH, the next time interval user 2 transmits, the next time interval user 1 transmits, and so forth. FIG. 6 is a simplification since more than one user can be scheduled in a TTI.
HSDPA achieves higher data speeds by shifting some of the radio resource coordination and management responsibilities to the base station from the radio network controller. Those responsibilities include one or more of the following (each briefly described below): shared channel transmission, higher order modulation, link adaptation, radio channel dependent scheduling, and hybrid-ARQ with soft combining.
In shared channel transmission, radio resources, like spreading code space and transmission power in the case of CDMA-based transmission, are shared between users using time multiplexing. A high speed-downlink shared channel is one example of shared channel transmission. One significant benefit of shared channel transmission is more efficient utilization of available code resources as compared to dedicated channels. Higher data rates may also be attained using higher order modulation, which is more bandwidth efficient than lower order modulation, when channel conditions are favorable.
The radio base station monitors for the carrier quality (CQI) of the high-speed downlink shared channel (HS-DSCH) and manages a priority queue maintained at the radio base station. The base station's priority queue (PQ) stores data which is to be sent on the high-speed downlink shared channel (HS-DSCH) over the air interface to the mobile terminal. In addition, knowing from the monitor the carrier quality of the HS-DSCH, the base station sends to the control node messages which authorize the control node to send more HS-DSCH data frames to the radio base station.
The mobile terminal reports a carrier quality indicator (CQI) to the radio base station in charge of the cell. The CQI is a measure of the quality of the common pilot CPICH as reported by each mobile station (e.g., each user equipment unit (“UE”)). The carrier quality indicator (CQI), together with an expression(s) of capabilities of the mobile terminal, is translated to a bitrate. The bitrate is then further reduced if needed by the radio base station, which results in generation of capacity allocation control frames which are sent to the control node regularly and/or per need bases, e.g. at urgent transitions. The authorizing messages include a “capacity allocation” which can be expressed in various ways, such as in terms of either bitrate or credits, for example. For example, capacity allocation expressed in credits may refer to a number of MAC-d PDUs that the radio network controller (RNC) is allowed to transmit for the MAC-d flow. In response to these authorizing messages, the control node sends further HS-DSCH frames to the radio base station.
The data in the priority queues is sent from a control node to a radio base station in protocol data units (PDUs). A number of PDUs may be included in each high-speed downlink shared channel (HS-DSCH) data frame.
Although HSDPA has been subject to much discussion, and the messages which transmit the capacity allocation have been standardized, no particular flow control algorithm for HSDPA has been standardized. See, e.g., 3GPP TS 25.435 V6.2.0 (2005-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iub Interface User Plane Protocols for Common Transport Channel Data Streams (Release 6), which is incorporated herein by reference in its entirety, including but not limited to §5.10 and §6.3.3.11 thereof which refer to HS-DSCH Capacity Allocation.
Some type of Iub Flow Control will have to be provided between RNC and RBS. Such Iub Flow Control will calculate the Capacity Allocation messages which are sent to the RNC, so that the RNC can send HS-DSCH Data Frames towards RBS according to the Capacity Allocations (CA), there being one Capacity Allocation for each flow (i.e., one Capacity Allocation for each priority queue flow (PQF)). Such Flow Control algorithm should ensure good end-user perceived data transmission.
A nominal Iub Flow Control approach assumes that the real user bitrate is what the Capacity Allocation control frames grant. In the nominal approach, the overall bit rate for the radio base station is equal to the sum of the fully allocated bit rates for each active flow. Since the bitrate for each flow is presumed in the nominal approach to be the full bitrate granted by the Capacity Allocation message, the bit rate for an individual flow is set to the Capacity Allocation for the respective flow.
In a HSDPA system there are generally two basic bottlenecks. One of the bottlenecks is on the downlink on the air-interface (Uu) between the radio base station node (RBS) and the mobile station; the other bottleneck is on the downlink on the interface (Iub) between the radio network controller node and the radio base station node. Both of these bottlenecks should be considered in a flow control algorithm. The available HS bandwidth over the Iub interface varies considerably. If too much HS traffic is allocated over Iub, frame losses and long delays degrade the HS packet data performance. The air interface scheduling of HS-DSCH Data Frames is controlled by the RBS.
When a priority queue flow (PQF) does not use the capacity allocated for it by its capacity allocation (CA) messages, then the Iub Transport Network will be under-utilized. The reason is that the PQF's share from the available capacity is reserved for the PQF, but it is not used.
There may be several reasons for why a Capacity Allocation bitrate is not fully used. As a first reason, the radio network controller (RNC) may limit the HSDPA HS-DSCH Data Frames bitrate with the RAB attribute “Iu Max bitrate” parameter (which could be set by operator as a function of subscription type, e.g. limited by operator to 64, 128 or 384 kbps or any other value (these examples just happen to be DCH bitrate look-alike limits)). As a second potential reason, there may be a bottleneck between the application server and SRNC, which could happen during certain time periods in some networks. A third plausible reason is that an application involved in the flow may not use more than a certain low bitrate during a certain period of time. A fourth possible reason is that traffic is bursty, e.g., one packet at a time (e.g. from a web page) is downloaded with big bitrate differences.
FIG. 7 illustrates that low bitrate bottlenecks are found ‘above’ the HSDPA Iub Flow Control Algorithm, i.e. above the radio network controller (RNC). The bottlenecks in the Application server, in the Serving RNC (SRNC) as the Iu Max Bitrate or the service network transport network in between those two nodes.
Thus, the nominal approach for HSDPA flow control does not consider situations where users in fact use much lower bitrates than granted in the Capacity Allocation messages. For example when a capacity allocation (CA) of 1 Mbps is sent to RNC, a user might use only 100 kbps.
The problem of the nominal HSPDA flow control approach is that capacity allocations (CAs) are reduced as a function of the active priority queue flows' capacity allocations. Capacity allocation (CA) bitrates are reduced if the total capacity allocation (CA) bitrates for all the active users are higher than the available Iub bitrate. This is done regardless of whether users are actually utilizing the full capacity allocation (CA) bitrate or not. As explained above, users not using the capacity allocation (CA) bitrate could be users with an application with limited bitrate, users experiencing a bottleneck anywhere between the ‘server’ and the RBS, or users limited by the RAB attribute Iu Max Bitrate.
FIG. 8A-FIG. 8D reflect a simulation example which illustrates problems with the nominal HSDPA Flow approach. In the simulation, there are ten users in a three-cell RBS, all of the users downloading large files. A new user arrives every twenty seconds until there are ten users in the system. Users 0, 3, 6, 9 reside in the first cell; users 1, 4, 7 reside in the second cell; while other users are in the third cell of the same RBS. All users are limited by Iu Max Bitrate 100 kbps except users 0 and 5. The RBS is connected to the radio network controller (RNC) using an E1 link.
FIG. 8A depicts the amount of transport network resources to be distributed and the sum of capacity allocation (CA) rates allocated for all priority queues (sumCAR). FIG. 8B shows incoming and outgoing PDU rate in the RBS. High initial Iub bitrate utilization occurs until later users enter the system, the later users not fully using their granted capacity allocation (CA). FIG. 8B depicts the incoming PDU rate to the RBS (in All), and the outgoing PDU rate from the RBS (out). The incoming bitrate of inactive users also depicted, but is zero in case of this simulation. It can be seen from FIG. 8B that at the beginning the rates are much higher than later. The later degradation of transport network utilization is caused by the users who do not use their allocated bandwidth. The average utilization of the transport network was also measured during the simulation and resulted in 62%.
FIG. 8C depicts average capacity allocation (CA) bitrate utilization for Priority Queue 0. In FIG. 8C and FIG. 8D, the Capacity allocated for the given user and the capacity used by the given user (Incoming PDU bitrate) is depicted for users 0 and 4, respectively. It can be seen that user 4 does not use more than 100 kbps capacity even if much more is allocated for user 4. On the other hand, user 0 uses all the capacity allocated to user 0, it is limited by its capacity allocation.
The foregoing simulation illustrates that the nominal HSDPA flow control approach cannot utilize the transport network resources in the case when some of the users do not use their allocated bandwidth.
What is needed, therefore, and an object herein provided for, are means, methods, and techniques for effectively utilizing transport network resources for a high-speed downlink shared channel (HS-DSCH) in the case when some of the users do not use their allocated bandwidth